SECTION 6. 9-PIN SERIAL INPUT/OUTPUT

1.Comma delineated ASCII - after every 32 characters.

2.Printable ASCII - after every line.

3.Binary - after every 256 Final Storage locations.

4.Tape - after every block (512 Final Storage locations).

6.5MODEM/TERMINAL PERIPHERALS

The CR10 considers any device with an asynchronous serial communications port which raises the Ring line (and holds it high until the ME line is raised) to be a modem peripheral. Modem/terminals include Campbell Scientific phone modems, and most computers, terminals, and modems using the SC32A Optically Isolated RS232 Interface.

When a modem raises the Ring line, the CR10 responds by raising the ME line. The CR10 must then receive carriage returns until it can establish baud rate. When the baud rate has been set, the CR10 sends a carriage return, line feed, "*".

The ME line is held high until the CR10 receives an "E" to exit telecommunications. The ME is also lowered if a character is not received after 40 seconds in the Telecommunications Command State (2 minutes in the Remote Keyboard State).

Some modems are quite noisy when not on line; it is possible for valid characters to appear in the noise pattern. For this reason, the CR10 counts all the invalid characters it receives from the time it answers a ring, and terminates communication (lowers the ME line and returns to the *0 Mode) after receiving 150 invalid characters.

6.6SYNCHRONOUS DEVICE COMMUNICATION

The CR10 differs from other Campbell Scientific dataloggers by its ability to address

Synchronous Devices (SDs). SDs differ from enabled peripherals (Section 6.2.1) in that they are not enabled solely by a hardware line. An SD is enabled by an address synchronously clocked from the CR10. Up to 16 SDs may be addressed by the CR10, requiring only three pins of the 9-pin connector.

Synchronous Device Communication (SDC) discussed here is for those peripherals which connect to the 9-pin serial port. This should not be confused with Synchronous Device for Measurement (SDM) peripherals connected to control ports 1, 2, and 3. (Although the communication protocol for SDMs is very similar, their addressing is independent of SDC addresses and they do not have a ring line.)

SD STATES

The CR10 and the SDs use a combination of the Ring, Clock Handshake (CLK/HS) and Synchronous Device Enable (SDE) lines to establish communication. The CR10 can put the SDs into one of six states.

STATE 1, the SD Reset State

The CR10 forces the SDs to the reset/request state by lowering the SDE and CLK/HS lines. The SD cannot drive the CLK/HS or RXD lines in State 1, however, it can raise the Ring line if service is needed. The SD can never pull the Ring low if a Modem/Terminal is holding it high. Data on TXD is ignored by the SD.

STATE 2, the SD Addressing State

The CR10 places the SDs in the addressing state by raising CLK/HS followed by or simultaneously raising SDE (Figure 6.6-1). TXD must be low while SDE and CLK/HS are changing to the high state.

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